As the nib of the pen bumped along the patterned napkin, the thin layers of material rose up like mountains on a snowy landscape.

"See this line on the left? That's the Black Sea," Tamir explained. "The line on the right is the Caspian. The Caucasus is in the middle."

Then came more lines, squiggles and arrows: bottom left - the Mediterranean, to which the Caucasus provides an outlet; bottom right - Iran and Turkey; dominating at the top - Russia.

I will never forget Tamir and his makeshift map, sketched for me in a cafe one afternoon in the North Caucasus.

Suddenly this little serviette had been transformed into a geopolitical paper napkin, reflecting thousands of years of turbulent history.

It helped explain why the Caucasus has been an age-old battleground, contested by the world's mightiest powers.

Among those who to have fought here are Alexander the Great, Genghis Khan and the Russian tsars.

The Caucasus has attracted empire-builders for both economic and political reasons.

Not only have the mountains offered an outlet to the Mediterranean Sea and acted as a corridor to eastern trade routes, they have also provided a natural security barrier.

'Achilles Heel'

For the last 150 years Moscow has been in control here - first the tsars, then the communists, and now President Vladimir Putin's Russia.

The ravages of war dominate the Chechen capital Grozny

Today, though, that control is being challenged.

A decade-long conflict in Chechnya has spilled over into other parts of the North Caucasus, the violence fuelled by a cocktail of corruption, widespread poverty, unemployment and militant Islam.

Following the Beslan school siege in 2004, in which more than 300 people were killed, the Kremlin accused "outside forces" of declaring war and of trying to tear the Caucasus away from Russia.

Tragedies on the scale of Beslan are rare, but there are almost daily reports from the region of bombings, shootings and clashes between militants and the security forces.

The North Caucasus is Russia's Achilles Heel. It is where Russia feels least confident, most at risk.

Patchwork of cultures

And yet away from all the instability, this is undoubtedly one of Russia's most beautiful regions.

The stunning peaks of the North Caucasus, together with the complex patchwork of local cultures and traditions have inspired some of Russia's greatest writers, such as Mikhail Lermontov and poet Alexander Pushkin.

This month I will be travelling across the North Caucasus, tracing the lines and contours on Tamir's map and trying to get a taste of what it is like to live on Russia's southern border.

I will be visiting towns and villages and meeting some of the dozens of ethnic groups which call the Caucasus their home.

Together, their traditions, their cultures, their spirit help them survive in Russia's most volatile region.

Steve Rosenberg will file several more features from the North Caucasus.